A predictive model of falling film evaporation with bubble nucleation on horizontal tubes

By comparing the experimental data with the predictions of the falling film evaporation models in the literature, the authors found that most of the existing models ignored the effect of nucleate boiling within the liquid film, which resulted in large prediction errors at high heat fluxes. A new predictive model is proposed to account for the nucleate boiling effect in falling film evaporation. This new model is based on the superposition model, but a new boiling correction factor is correlated from the experimental data of falling film evaporation using refrigerants. The new model predicts the falling film evaporation data of horizontal plain tubes at 2-100 kW/m² heat flux using R-11, R-123, R-134a, R-141b, and R-22 with −20+25% prediction errors and 12.9% root mean square deviation. This model is also applied to correlate the boiling correction factor of a boiling enhanced (Turbo-B) tube, and it predicts the falling film evaporation data of the Turbo-B tube at 19-40 kW/m² heat flux using R-123, R-134a, and R-22 with −30%+33% prediction errors and 13.9% root mean square deviation.